A hummingbird's long bill and tongue evolved to let the bird reach deep into a flower for nectar.
Natural selection is the engine that drives evolution. The organisms best suited to survive in their particular circumstances have a greater chance of passing their traits on to the next generation.
But plants and animals interact in very complex ways with other organisms and their environment. These factors work together to produce the amazingly diverse range of life forms present on Earth.
The concept of fitness is central to natural selection. In broad terms, individuals that are more “fit ” have better potential for survival, as in the well – known phrase “survival of the fittest”. Natural selection is a process by which heritable traits that are helpful for survival and reproduction become more common in a population, while harmful traits become more rare. This occurs because individuals with advantageous traits reproduce more successfully, so that more in the next generation inherit these traits. Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of those variants best – suited for their environment.